1. Field of the Invention
The present invention relates to a circuit device and, more particularly, to a circuit device using a metal substrate.
2. Description of the Related Art
In recent years, as circuit devices incorporated in electronic equipment and the like have become smaller in size, higher-density and more functionally-sophisticated (e.g., multi-functional), the heat generation density per unit volume of a circuit device has been on the rise. To cope with this trend, metal substrates, which excel in their heat release performance, are today often used as substrates for the circuit devices, and at the same time circuit elements, such as ICs (Integrated Circuits) or LSIs (Large Scale Integrated Circuits) are mounted on such metal substrates (See Reference (1) in the following Related Art List, for instance).
FIG. 10 is a sectional view schematically illustrating a structure of a conventional circuit device as disclosed in Reference (1). In FIG. 10, a metal base plate 103 provided with a first insulating layer 104 and a first circuit pattern 105 on the top thereof constitutes a metal substrate 120. Power elements 106 are disposed on the metal base plate 103 through the intermediary of the first insulating layer 104 and the first circuit pattern 105. The power elements 106 and the first circuit pattern 105 are electrically connected with each other via wires 107. Further, in such a conventional circuit device, the metal base plate 103 is divided into regions thereof, on each of which a power element 106 and a first circuit pattern 105 connected thereto are disposed, and a second insulating layer 108 is disposed between the adjacent regions.
3. Related Art List
(1) Japanese Patent Application Laid-Open No. Hei11-074452.
In the above-cited conventional structure, a plurality of power elements 106 are each disposed on a metal base plate 103 through a first insulating layer 104. Accordingly, the heat generated by a power element 106 is released to the metal base plate 103 through the first insulating layer 104 which is in the region where the power element 106 is mounted. However, a problem in this setup is that because of a large thermal resistance of the first insulating layer 104, the heat generated by the power element 106 is not sufficiently released to the metal base plate 103.
Another problem in this setup is that heat is also generated at a portion of the first circuit pattern (pad electrode portion), which is connected to a power element 106 via a wire 107, but because of a large thermal resistance of the first insulating layer 104 located thereunder, the heat generated is not sufficiently released to the metal base plate 103.